New evidence indicates that there is a significant increase in the number of hypopneas and apneas during sleep in the elderly. Almost all of these respiratory irregularities are terminated by transient arousals. These findings indicate that age-related respiratory impairments may account for much of the sleep fragmentation reported for elderly subjects. The frequency and duration of the apneas and hypopneas are often severe enough, even in subjects with no sleep complaints, to be classified as sleep apnea syndrome. Since the anoxia and hemodynamic alterations resulting from this syndrome may be a major source of morbidity and mortality in the aged, it is important to try to shed light on the mechanisms underlying these respiratory impairments. One possibility is that they are due to changes or defects in respiratory regulation during sleep, or to a partial dissociation between ventilatory and arousal responses to respiratory stimuli. At present, however, little is known about the effect of age on these processes. This proposal seeks to provide a systematic study of respiration and its regulation during sleep in the aged. Toward this aim, alveolar CO2 tension, oxygen saturation, tidal volume, ventilation, respiratory rate and abdominalthoracic respiratory movement will be measured along with EEG, EOG and EMG during all night sleep runs in elderly subjects and also in younger controls. Additionally, hypoxic response tests and CO2 sensitivity tests will be carried out on the same groups during all-night sleep runs. Results of this study will provide new knowledge on the effect of aging on chemical regulation of respiration during sleep, on interactions between the respiratory centers and the ascending reticular activating system (ARAS), and on some aspects of respiratory rhythm (pattern, rate, tidal volume).